Stiff hingeless rotors commonly found on high speed vertical takeoff and landing (VTOL) aircraft are relatively unstable in terms of, e.g., pitch moment versus angle of attack. A relatively large horizontal stabilizer may be required to provide restoring force to counteract this instability. The stabilizer itself is typically associated with a weight penalty, in addition to weight penalties in the tail cone and the rotor to react to large stabilizer loads. There may also be a drag penalty for the large stabilizer, as well as the center of gravity (CG) being pushed aft.
Conventional control systems have used stability augmentation systems (SAS) that sense angular aircraft rate feedback to increase stability. In other instances, angular acceleration feedback was used to improve stability. Differentiation of angular rate provides an acceleration signal with significant noise content. Filtering may enhance the signal-to-noise ratio (SNR) of the acceleration signal so as to be useful, but it may limit the effectiveness of the acceleration feedback to enhance aircraft stability.